The present invention relates to a dielectric ceramic composition useful for a device used as a resonator, a filter, an antenna, a capacitor, an inductor, a circuit board or the like in a high frequency band such as microwave, millimeter wave, etc. The present invention also relates to a device for a communication apparatus including such a dielectric ceramic composition.
Recently, dielectric ceramics have been used widely as filter materials for communication apparatus with the spread of mobile communication. Such dielectric ceramics are required to have a low dielectric loss (tan xcex4), i.e. a high Q value that is the inverse of the dielectric loss, a small absolute value of the temperature coefficient at capacitance (TCC), and a high transverse strength.
It is predicted that the frequency of communication systems will become higher and the shorter wavelength of the radio wave will be used. Therefore, when machining accuracy and conductor loss are taken into account, dielectrics having a low dielectric constant increasingly will be demanded. As an example of a conventional dielectric ceramic composition having a low dielectric constant, a dielectric ceramic composition in which glass is added to AL2O3 is proposed in, for example, JP 62 (1988)-173797A. As another example of a conventional dielectric ceramic composition having a low dielectric constant, a dielectric ceramic composition in which glass is added to AL2O3 is proposed in, for example, JP 11 (1999)-228216A.
However, the dielectric ceramic composition in which glass is added to Al2O3 has a low dielectric constant of 10 or less, but has a large TCC of about 100 ppm/xc2x0 C. Under such circumstances, a dielectric ceramic composition having a dielectric constant that is at the same level or less than that of this type of dielectric ceramic composition and the TCC being close to zero has been demanded. The present inventors previously proposed a dielectric ceramic composition having a low dielectric constant, a low loss, and a small absolute value of the temperature coefficient at resonance frequency (TCF) in JP11 (1999)-228216A. However, dielectric ceramic compositions having a lower dielectric constant, a higher Q value that is the inverse of the dielectric loss (tan xcex4), and a smaller absolute value of the temperature coefficient at capacitance (TCC) have been demanded.
It is therefore an object of the present invention to provide a dielectric ceramic composition capable of being fired at a low temperature and stably having high strength and yet having a lower dielectric constant, a higher Q value that is the inverse of the dielectric loss (tan xcex4), and a smaller absolute value of the temperature coefficient at capacitance (TCC) as compared with the conventional dielectric ceramic composition, and to provide a device for a communication apparatus using this dielectric ceramic composition suitably in a high frequency band such as microwave, millimeter wave, etc.
In order to achieve the above-mentioned object, the dielectric ceramic composition of the present invention includes at least a first component containing Al2O3, MgO and ROa (R is at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb and Gd; a is a value stoichiometrically determined in accordance with the valence of R); SiO2 as a second component; and a third component containing a glass composition including two or more components containing at least one selected from the group consisting of SiO2 and B2O3.
Next, a method for producing a dielectric ceramic composition of the present invention includes melting by preliminarily heating a third component including two or more components containing at least one selected from SiO2 and B2O3 and then quenching to form a glass composition; pelletizing and mixing a predetermined amount of a first component including Al2O3, MgO and ROa (R is at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb and Gd, a is a value stoichiometrically determined in accordance with the valence of R), a second component including SiO2; and the third component; granulating the mixture and then molding the granulated product; preheat treating the molded product and then principally firing the product.
Next, a device for a communication apparatus of the present invention uses a dielectric ceramic composition including at least a first component containing Al2O3, MgO and ROa (R is at least one element selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Tb and Gd; a is a value stoichiometrically determined in accordance with the valence of R); a second component, SiO2; and a third component containing a glass composition including two or more components containing at least one selected from the group consisting of SiO2 and B2O3.